1. Field of the Invention
The invention relates to a hot stamping method and to a hot stamping device particularly suitable for performing the method.
2. Description of the Prior Art
Hot stamping or embossing methods and devices of this type are used for the hot stamping or embossing of material layers to be stamped with stamping product on a stamping foil web. The material layer, also referred to as printing material and which can be a sheet or a web material, is moved at a normally uniform material layer speed through a stamping gap and the stamping foil web is jointly moved in such a way that a stamping foil web portion during a stamping interval moves at the same speed as the material layer through the stamping gap. This is necessary so that the stamping product, which can be discreet, juxtaposed or successively arranged stamping units such as images, texts, etc., or parts to be stamped on or areas of ink or colour coatings, can pass in undistorted and unsmeared manner onto the material layer to be stamped and consequently the stamping foil web does not tear during the stamping interval.
In order to minimize waste of the often expensive stamping foil or film material, in the case of stamping foils the aim is to keep as small as possible the unused or unstamped foil web areas. It has already been proposed for this purpose to bring successively positioned stamping product areas to be stamped on the stamping foil web closer together than successive stamping locations on the material web. This can be brought about in that the stamping foil web outside a stamping interval is moved at least temporarily at a foil web speed differing from the material layer speed. The necessary speed changes to the stamping foil web can be obtained by foil accelerating means and a foil acceleration can be both a speed increase/decrease and a direction reversal of the stamping foil web movement.
A hot stamping rotary press providing a feed speed rise upstream of a stamping interval and a feed speed drop after a stamping interval with respect to the stamping foil is disclosed by DE 29 31 194. In this case the stamping foil web is always moved in the main movement direction thereof, the speed in said direction varying and never being higher than the material layer speed.
To reduce the accelerative forces acting on the possibly tension-sensitive stamping foil web, DE 37 13 666 already proposes to pull back by a certain amount the stamping foil web upstream of every new stamping interval, so as to permit a longer starting distance and optionally also a longer decelerating distance, so that acceleration strains on the stamping foil web can be reduced. Here again the foil web speed in the main conveying direction at no time exceeds the material layer speed.
The object of the invention is to so further develop hot stamping methods and devices of the aforementioned type that there is a particularly effective utilization of the stamping product on the stamping foil web.
For solving this problem the invention proposes a hot stamping method for stamping material layers with a stamping product present on a stamping foil web, in which a material layer is moved at a material layer speed through the stamping gap and the stamping foil web is jointly moved in such a way that a stamping foil web portion during a stamping interval is moved at the same speed as the material layer through the stamping gap whereas, outside a stamping interval, the stamping foil web portion is at least temporarily moved at a foil web speed differing from the material layer speed, wherein the following steps are provided:
stamping a first stamping product area of the stamping foil web during a first stamping interval at a first stamping location,
stamping a second stamping product area, following the first stamping product area in the web direction, during a following, second stamping interval at a second stamping location,
acceleration of the stamping foil web between the first and second stamping intervals in such a way that a space between succeeding stamping product areas of the stamping foil web is larger than an unstamped area between associated, succeeding stamping locations of the material layer. There is further provided hot stamping device comprising:
a stamping press, in which between a cylinder and a movable back pressure element, a stamping gap is formed at least during a stamping interval, and
foil conveying means for producing, at least during a stamping interval, a speed of a stamping foil web portion with being the same as the speed of a material layer moved with a material layer speed through the stamping gap,
the foil conveying means being constructed as foil acceleration means in such a way that the stamping foil web portion, outside the stamping intervals, at least temporarily is movable with a foil web speed differing from the material layer speed;
wherein the stamping foil web can be accelerated by the foil accelerating means between a first stamping interval and a following, second stamping interval in such a way that a space provided with the stamping product between succeeding stamping product areas of the stamping foil web delivering stamping product is larger than an unstamped area between associated, succeeding, stamping product-receiving stamping locations on the material layer and which is particularly suitable for performing this method. Preferred further developments are given in the dependent claims. By reference the wording of all the claims is made into part of the content of the description.
A hot stamping method according to the invention is characterized in that at least once during a stamping pass during a first stamping interval a first stamping product area of the stamping foil web is stamped at a first stamping location of a material layer, that during an immediately following, second stamping interval on a second stamping location of a material layer is stamped a second stamping product area of the stamping foil web following the first stamping product area in the web direction and that between these stamping intervals the stamping foil web is accelerated in such a way that between the successive stamping product areas of the stamping foil web is formed a gap or space still provided with the stamping product and which, measured in the web direction, is larger than an unstamped area between the succeeding stamping locations on the material layer. For this purpose and diverging from all known solutions, the stamping foil web in the acceleration phase between the succeeding stamping intervals is moved at least temporarily in the main movement direction of the stamping foil web at a web speed which is higher than the normally uniform material layer speed. The web speed can e.g. be more than 5, 10 or 20% higher than the material layer speed, but is in general less than 50% higher. In the acceleration phase there is at least one deceleration or speed reduction of the stamping foil web to ensure that the latter in the stamping interval following the acceleration phase moves at the same speed as the material layer. The speed rise and speed drop are matched to one another in such a way that in the acceleration period between the stamping intervals a stamping foil web portion is moved through the stamping gap whose length exceeds the length of the material layer portion passing at the same time through the stamping gap.
As a result of this apparently contradictory measure with respect to the sought minimizing of foil web waste, it is possible to ensure that the space between the directly succeeding, already stamped stamping product areas is increased compared with the spacing of the associated stamping locations to such an extent that in a time-succeeding stamping step it is still possible to stamp stamping product from this enlarged intermediate area. A gap between succeeding stamping product areas, which is e.g. too small to enable to make economies according to the above-described, conventional methods, can also be deliberately stretched or lengthened somewhat in order to utilize the increased gap for at least one further stamping operation. The foil consumption is consequently initially deliberately locally increased and then subsequently, whilst utilizing the stamping product in the gap, to bring about overall a very effective surface utilization of the stamping product present on the stamping foil web.
The following utilization of the stamping product located in the area of the gap resulting by a deliberate size increase between the successive stamping product areas, can take place in a separate pass of the stamping foil web, optionally after winding back said stamping foil web onto a wind-off reel. However, preferably the stamping product present in the gaps is stamped in the same stamping foil pass as the stamping product in the stamping product areas bounding the gaps in the web direction. For this purpose in a preferred further development of the method there is a limited drawing back movement of the stamping foil web counter to the main movement direction following a second stamping interval and a subsequent acceleration of the stamping foil web in the main movement direction in such a way that in a third stamping interval following the second stamping interval stamping product can be transferred from the gap to the material layer. Thus, after the drawing back movement, the stretched gap area passes at least a second time through the stamping gap and during said second pass the stamping foil web is so longitudinally displaced in the web direction compared with the first pass that stamping product present in the gap can be transferred by a stamping die to the material layer.
To the extent that the printing material is in the form of successive, individual sheets, it is appropriate to coordinate the time of the drawing back movement with the passage of the sheets in such a way that said movement at least temporarily takes place during the transition between successive individual sheets through the stamping gap. Since normally between directly succeeding individual sheets a certain spacing occurs, necessarily between succeeding sheets there is a stamping pause, which is at least as long as the time elapsing between the passage of the rear edge of a leading sheet and the passage of the front edge of a directly following sheet through the stamping gap. Thus, generally more time is available for the necessary acceleration movements, so that only smaller acceleration levels and correspondingly smaller forces acting on the sensitive stamping foil sheet are necessary. Generally and in particular when printing material layers in web form, the drawing back movement is so appropriately matched to the material run and the spacing sequence of successive stamping locations, that the drawing back movement takes place at the same time as the passage of the largest stamping location spacing in the running direction. There is no need for a drawing back movement after each sheet which has passed through or after every particularly large stamping location spacing and instead it can take place in irregular manner.
A further development is particularly advantageous if succeeding stamping product areas have essentially the same shape and size. In this further development the acceleration of the stamping foil web is carried out in such a way that the enlarged gap is so dimensioned that from the area of the gap successively at least one stamping product area can be stamped having substantially identical dimensions to the stamping product areas bounding the gap. To avoid excessive accelerations the procedure is preferably such that precisely one stamping product area is positioned in the gap and preferably symmetrically between the bounding stamping product areas. Thus, here the gap size, i.e. the extension of the gap in the longitudinal direction, is larger or at the most the same as the running direction extension of the succeeding stamping product areas, which generally have a small mutual spacing in order to ensure edge-sharp stampings. However, it would also be possible to dimension the gap so as to be shorter than the longitudinal extension of the stamping areas bounding it. It would still be possible to stamp from said gap stamping product areas which particularly in the longitudinal direction are smaller than the stamping areas bounding the gap.
It can arise that the stamping locations on the material layer to be stamped have non-uniform, mutual spacings. Particularly for such cases it can be provided that the acceleration of the stamping foil web is performed in such a way that the spacings between succeeding, stamped, stamping product areas are substantially the same. After this rendering uniform of the spacings between stamped stamping areas between the already stamped stamping product areas of the stamping foil web there are substantially identically dimensioned gaps and for this purpose part of the gaps is enlarged and another part of the gaps is correspondingly size-reduced.
The invention also relates to a hot stamping device suitable and adapted to the performance of said hot stamping method. It has a stamping press in which between a cylinder and a movable back pressure element, particularly a back pressure cylinder, a stamping gap is formed at least during a stamping interval. It has foil conveying means for producing at least during a stamping interval an identical-speed following of a stamping foil web portion with a material layer portion moved through the stamping gap and which is normally moved with a uniform speed by suitable material layer conveying means through said gap. The foil conveying means are constructed as foil accelerating means and can consequently produce a discontinuous conveying of the stamping foil web or a non-uniform following with the material layer. The foil accelerating means are constructed in such a way that the stamping foil web between a first stamping interval and a directly following, second stamping interval can be accelerated in such a way that a space provided with a not yet stamped stamping product between succeeding stamping areas of the stamping foil web delivering the stamping product is larger than an unstamped area between succeeding stamping locations on the material layer receiving the stamping product.
As stated, the foil accelerating means are so designed and controlled that during the acceleration phase the stamping foil web at least temporarily is moved with a higher web speed in the main conveying direction than the material layer. Appropriately the foil accelerating means for producing a forward/return step operation are designed so as to be able to perform the aforementioned stamping foil web drawing back movements. Although a purely electronic control of the foil accelerating means is possible, it is appropriate for controlling the latter to provide a computer unit, so that with the aid of the foil accelerating means and corresponding computer unit operating programs preset speed profiles are produced for the stamping foil web.
With respect to the construction of the stamping press and the foil conveying means the hot stamping device can e.g. be constructed in the same way as the stamping rotary press described in EP 718 099. Correspondingly the foil conveying means for an individual foil web can have a pulling device following the stamping gap and e.g. operating with a suction belt with a slip drive for the stamping foil web and a controllable foil feed device upstream of the stamping gap and cooperating with the pulling device. The foil feed device can have at least one control roller in rolling contact with the stamping foil web and controllable by a control mechanism with respect to the rotational speed and/or rotation direction and which can also be constructed as a suction roller and allows no slip in the stamping foil web direction, so that through the foil feed device it is possible to fix the precise position and speed of the stamping foil web in the or counter to the conveying direction. As a result of the e.g. computer-assisted control of the control roller, it is possible to implement inventive foil speed profiles.